Bathroom scales are well known, particularly those of the relatively flat type as illustrated in U.S. Pat. No. 3,547,212 having a platform overlying a weighing mechanism contained within a generally flat housing. The weighing mechanism converts the force produced by a person standing on the platform to a rotation of an output shaft in proportion to the person's weight. This output shaft rotation in conventional bathroom scales moves a scale disc past a window to indicate the weight of the person standing on the scale.
Bathroom scales in which an output shaft rotation is automatically sensed to provide an illuminated numerical display with an indication of the correct weight are known. See, for example, the U.S. Pat. No. 3,853,191 to Yamagiwa.
In this patent a weighing machine is shown and described with a digital display activated from an AC line source. An optically decodable encoder wheel is used and mounted on a shaft whose rotation is proportional to the weight measured by the scale. An optical reader is employed to detect the amount of rotation by sensing the optical codings on the encoder wheel and then generate an appropriate signal to a numerical display. Appropriate switches are used so that the device will not be electrically activated unless a weighing operation is actually being made.
The optically encoded wheel described in the Yamagiwa patent has a disadvantage in that several optical transitions between successive numerical positions of the code wheel may occur. Thus, if the scale happens to come to rest directly opposite such transition, an uncertainty in the numerical read-out is likely to occur, causing large variations in the weight indication.
Such uncertainty problem with optical encoders has been recognized and a so-called Gray code developed to avoid having more than a single optical transition between successive numerically different weight indicating positions. The optical scales shown and escribed in the U.S. Pat. Nos. 3,061,026 and 3,627,069 are exemplary of the use of such a binary optical code. In these patents the optical binary encodings are arranged in channels with the channel representative of the least significant increment representing a binary fraction. Only one channel has an optical transition between successive weight indicating positions within the weighing range of the scale.
A binary Gray code, as for example illustrated in U.S. Pat. No. 3,627,069, can be converted to a conventional, 8, 4, 2, 1 straight binary code by using a well-known technique involving exclusive OR circuits. These are each responsive to a binary digit in the Gray code and are interconnected in such manner as to generate the straight binary code.
The latter binary code is then, in turn, converted to a binary decimal code (bcd) in order to operate normally available numerical displays. Techniques and devices to provide this conversion are well known, but involve additional circuitry, thus adding to the cost of the optical encoder used in the bathroom scale.